Communication between PC and Controller

COM technology

The PC SDK uses an internal Controller API based on COM technology to communicate with the controller. This API uses sockets and the local TCP/IP stack (see Definitions) towards both real and virtual controllers.

Note

You should be aware that the .NET garbage collector does not collect COM objects, but these need to be disposed of explicitly by the application programmer. For more information, see Accessing the controller.

Resource identification

All controller resources, both real and virtual, are described using object based hierarchy. Each resource is uniquely identified, including information about which controller owns the resource by use of the unique system id or IP address of the controller.

The controller is the top object of the hierarchy: /<Controller>/<Domain>/<SubDomain1>/<SubDomain2>/ and so on.

Error messages including such a path indicate the location of the problem.

Hard real-time demands

The PC Controller API cannot meet hard real-time demands for the following reasons:

• Part of the API executes on a non-real-time operating system.

• Communication is performed with TCP/IP over a network.

• The controller sometimes has tasks to perform that have a higher right of priority.

Note

A minimum response time for real controllers should be expected to be in the order of 10-100 milliseconds.